(a) Field of the Invention
The present invention relates to a thrust magnetic bearing for bias compensation, and more particularly, to a thrust magnetic bearing for bias compensation in which annular permanent magnets and electromagnets are disposed to face each other with respect to a levitated member, and the permanent magnets are formed to be asymmetrical in lengths thereof in an axial direction to thus compensate for a bias by the difference in the lengths of the permanent magnets in the axial direction.
(b) Description of the Related Art
Related art general bearings frictionally contact with each other, and thus, magnetic bearings minimizing frictional contact have been commonly used in various fields.
As disclosed in Korean Patent Laid-Open Publication No. 2009-0070178 (Entitled: “Cylindrical System For Measuring Displacement In Radial Direction of Magnetic Bearing Using Capacitance And Method For Determining Fault Thereof”, Publication Date: 2009 Jul. 1), magnets or electromagnets assuming strong magnetism are disposed on the circumference of a rotational shaft and levitated member floats the rotational shaft by magnetic levitation to serve as a bearing.
The magnetic bearing described above is advantageous in that, since it is not in contact with the shaft or the levitated member, frictional contact is eliminated, and since components thereof are not worn and damaged, high durability thereof is obtained and less noise is created.
FIG. 1 is a view illustrating an example of a related art active thrust magnetic bearing in which a levitated member is supported only by electromagnets.
The active thrust magnetic bearing illustrated in FIG. 1 uniformly maintains a position of a levitated member by adjusting an amount of current supplied to an electromagnetic coil according to positions of the levitated member.
However, in the active thrust magnetic bearing illustrated in FIG. 1, since bias magnetic force needs to be applied to the levitated member in advance, a constant bias current should be continuously supplied, causing high energy loss to degrade efficiency and cause an excessive temperature increase.
FIG. 2 is a view illustrating an example of a related art hybrid thrust magnetic bearing in which electromagnets support a levitated member together with permanent magnets.
The hybrid thrust magnetic bearing in which electromagnets and permanent magnets are provided together illustrated in FIG. 2 has been devised to overcome the shortcomings of the active thrust magnetic bearing illustrated in FIG. 1. In the hybrid thrust magnetic bearing, a bias magnetic force is formed in advance using the annular permanent magnets, and a position of the levitated member is controlled by adjusting an amount of current applied to the electromagnets.
In the hybrid thrust magnetic bearing in which the electromagnets and permanent magnets are provided together as illustrated in FIG. 2, since a current supply for bias magnetic flux is not required, energy may be saved and a temperature increase is low.
However, as illustrated in FIG. 3, in the hybrid thrust magnetic bearing in which the electromagnets and permanent magnets are provided together, in a case in which a shaft is disposed in a longitudinal direction and a permanent magnet cannot be attached to a rotor, in particular, to an upper surface of the rotor supported by a magnetic bearing, current for compensating for gravitational force should be continuously supplied.
In detail, in the case of the rotor disposed in a longitudinal direction and supported by a magnetic bearing, generally, a permanent magnet is disposed on an upper surface of the rotor in order to compensate for gravitational force acting on the rotor by using attractive force of the permanent magnet.
However, in a device such as a turbo machine in which an impeller is attached to an upper portion thereof or a device such as a centrifugal separator in which a bucket is attached to an upper portion thereof, a permanent magnet for compensating for gravitational force of a rotor cannot be attached to an upper portion of the rotor.
Therefore, in order to solve this problem, a current should be continuously supplied to compensate for gravitational force of the rotor, which results in a large amount of energy loss and a significant temperature increase.